package network;

import javax.lang.model.element.NestingKind;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    //通过 start 启动服务器的核心流程
    public void start() throws IOException {
        System.out.println("服务器启动");
        while (true) {
            //此处通过 死循环 不停的处理客户端的请求

            //1.读取客户端的请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //将二进制byte转为字符串,方便输出
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());

            //2.根据请求计算响应,由于此处是回显服务器,响应就是请求.
            String response = process(request);

            //3.把响应写回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);

            //4.把日志打印一下
            System.out.printf("[%s:%d] req=%s,resp=%s\n",requestPacket.getAddress(),
                    requestPacket.getPort(),request,response);
        }
    }

    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
